Apple announced a policy change with respect to Apps hosted outside the Mac App Store, where all such Apps must be notarized by Apple in order to run by default on MacOS Catallina (v10.15.5) and later. See https://developer.apple.com/news/?id=12232019a for details.
Users attempting to install the PKI Client package for MacOS, get shown a warning pop-up message indicating the package can’t be opened because Apple is not able to check whether it contains malicious software, and can’t proceed with the installation of the PKI Client package:
The below steps provide a solution to allow you to continue with the installation of the PKI Client package.
If you have any questions please contact DigiCert Platform PKI support by going to the below link;